Abstract
AbstractProposals for systems embodying condensed matter spin qubits cover a very wide range of length scales, from atomic defects in semiconductors all the way to micron-sized lithographically defined structures. Intermediate scale molecular components exhibit advantages of both limits: like atomic defects, large numbers of identical components can be fabricated; as for lithographically defined structures, each component can be tailored to optimise properties such as quantum coherence. Here we demonstrate what is perhaps the most potent advantage of molecular spin qubits, the scalability of quantum information processing structures using bottom-up chemical self-assembly. Using Cr7Ni spin qubit building blocks, we have constructed several families of two-qubit molecular structures with a range of linking strategies. For each family, long coherence times are preserved, and we demonstrate control over the inter-qubit quantum interactions that can be used to mediate two-qubit quantum gates.
Highlights
Among the molecular spin systems that have been proposed as qubit candidates are N@C60,6–9 organic radicals10,11 and molecular magnets
We proposed exploiting molecular magnets based on heterometallic antiferromagnetic rings
Phase relaxation times in heterometallic antiferromagnetic rings are in the 1–10 μs range at low temperatures,18,19 and they can be manipulated in a typical pulsed electron spin resonance (ESR) apparatus on the 10-ns timescale; an interaction offering h/J in the 100-ns range could be exploited, for example, in a multiqubit experiment to generate controlled entanglement
Summary
An information processing device whose elements are capable of storing and processing quantum superposition states (a quantum computer) would support algorithms for useful tasks such as searching and factoring that are much more efficient than the corresponding classical algorithms, and would allow efficient simulation of other quantum systems. One of the key challenges in realizing a quantum computer lies in identifying a physical system that hosts quantum states sufficiently coherently, and provides appropriate interactions for implementing logic operations. Among the molecular spin systems that have been proposed as qubit candidates are N@C60,6–9 organic radicals and molecular magnets. We proposed exploiting molecular magnets based on heterometallic antiferromagnetic rings.15,16These systems exhibit a number of favourable features supporting their application as components of a quantum computer: flexibility in their chemical composition allows control over both the total ground-state spin (by modifying the heteroatom) and the carboxylate ligands; their well-defined internal magnetic excitations may offer mechanisms for efficient single-qubit manipulations; and the ground-state spin is highly coherent, when the chemical structure is optimised.19In the context of molecular spin qubits, the simplest conceivable multi-qubit structure is a molecular dimer. We proposed exploiting molecular magnets based on heterometallic antiferromagnetic rings.15,16 These systems exhibit a number of favourable features supporting their application as components of a quantum computer: flexibility in their chemical composition allows control over both the total ground-state spin (by modifying the heteroatom) and the carboxylate ligands; their well-defined internal magnetic excitations may offer mechanisms for efficient single-qubit manipulations; and the ground-state spin is highly coherent, when the chemical structure is optimised.. Phase relaxation times in heterometallic antiferromagnetic rings are in the 1–10 μs range at low temperatures, and they can be manipulated in a typical pulsed electron spin resonance (ESR) apparatus on the 10-ns timescale; an interaction offering h/J in the 100-ns range could be exploited, for example, in a multiqubit experiment to generate controlled entanglement. This allows us the flexibility to optimise the physical properties of the dimers with respect to the three key time scales
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